For welding operations in which the actual welding area is to be covered with an inert shielding gas, it is usual to obtain the shielding gas from a supply unit where the gas is at a relatively high pressure. It is therefore usual to install a regulator valve in the supply line in fairly close proximity to the point at which the actual welding apparatus is located, and to control the flow rate by means of a flow valve which is normally fitted on the supply line immediately after the regulator valve. When a wire welding apparatus is used, the welding apparatus will also be equipped with a simple on/off gas supply valve which admits the flow of shielding gas to the welding gun when an operator starts a welding operation, and shuts off the flow of gas to the welding gun when the operator finishes the welding operation. Adjustment of the flow rate is usually made by manual adjustment of the flow valve, and will depend upon a number of factors that are associated with the welding work to be done. These factors may, for example, be the character of the welding wire, the geometry of the welding gun nozzle and/or the welding current the operator is going to use. To achieve a completed welding job of a particular quality, it is of utmost importance that the operator should make the correct adjustment of the regulator valve, and even more important is the correct adjustment of the flow valve. A typical system that is used at present is shown in FIG. 1 of the attached drawings.
As can be seen from FIG. 1, a first length of supply line will typically be located between the gas tank (or gas supply unit) and the point at which the regulator valve and flow valve are located. A second (in this instance substantial) length of supply line will be located between the point at which the regulator valve and the flow valve are located and the position of the gas supply valve (which typically is an integral part of the main unit of the welding apparatus), whilst a third length of supply line will be located between the gas supply valve and the actual welding gun nozzle from where the gas can exit freely in order to flow out over the weld. From this it follows that both before the start of a welding operation and after the completion of a welding operation, an “overpressure” will build up in the second length of the supply line, which “overpressure” corresponds to the pressure set in the regulator valve. When a welding operation is commenced and the gas supply valve opens, this “overpressure” will result in an immediate and forceful emission of gas which, after the “overpressure” has been relieved, will take on a flow rate that is determined by the setting of the flow valve. When the operator has to carry out his welding in the form of many welding operations of short duration, this results in frequent “blow-outs” which cause both a substantial increase in gas consumption and undesirable flow conditions at the gas outlet of the welding gun nozzle.
Another factor that is of importance for the quality of a welding job is that the flow rate is set correctly in relation to other welding parameters, as mentioned above. Whilst carrying out a welding operation, a welding operator will typically make in-process adjustments of settings that affect the feeding speed of the welding wire and/or the value of the welding current. When these parameters are changed, corresponding changes should be made in the shielding gas flow rate. In practice, changes of the shielding gas flow rate are rarely made, partly because the controls for the adjustment of the welding wire feeding speed and/or the welding current are typically located on the main part of the welding apparatus, which in the case of large welding units are often located some distance from the position of the flow valve, and partly because this means yet another operation for the operator. The operator may then for his own convenience first set the flow rate which in any case is high enough to meet all needs, and this in turn may result in the use of an unnecessarily high flow rate and thus an “over-consumption” of the expensive shielding gas.
Patent documents DE 3544280, EP 2860974, U.S. Pat. No. 3,811,027, U.S. Pat. No. 4,278,864, U.S. Pat. No. 5,017,757 and U.S. Pat. No. 5,772,102 all concern techniques that are related to electric welding, and to a varying degree all deal with the problems concerning shielding gas. However, none of these documents seem to disclose the features that characterise the present invention or to address the aforementioned matters by providing a solution that corresponds to any of the solutions of the present invention.
On the basis of the matters mentioned above, there is a need for a solution that will, without any input from the operator, adjust the flow rate of the shielding gas continuously during the performance of a welding job, and control the flow rate of the shielding gas, thereby reducing the total gas consumption.
Accordingly, the object of the invention is to provide solutions whereby improvements of the control of the shielding gas supply in a welding apparatus are obtained.